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Proceedings of SPIE, the International Society for Optical Engineering/Proceedings of SPIE

Single-photon source using stimulated FWM in optical fibers for quantum communication

Álvaro J. Almeida, Nuno A. Silva, Nelson Jesus Muga, Armando N. Pinto

Published May 21, 2011• 5 citations
Publisher

Abstract

A single-photon source based on the stimulated four-wave mixing (SFWM) process in optical fibers is presented. At the output of the source, the state of polarization (SOP) of the photons can be adjusted in order to obtain any linear polarization. A theoretical model to describe the average photon counts recorded in the avalanche photodiodes (APDs) is presented. The experimental results show an accurate detection of two non-orthogonal linear SOPs after propagation through a 60 km quantum channel, and good agreement with theory. This source, operating in a low power regime, can be used for quantum key distribution (QKD) using polarization-encoding in quantum communications.

DOI
10.1117/12.891915

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Proceedings of SPIE, the International Society for Optical Engineering/Proceedings of SPIE•Feb 20, 2017•0 citations
A single-photon source based on the stimulated four-wave mixing (SFWM) process in optical fibers is presented. At the output of the source, the state of polarization (SOP) of the photons can be adjusted in order to obtain any linear polarization. A theoretical model to describe the average photon counts recorded in the avalanche photodiodes (APDs) is presented. The experimental results show an accurate detection of two non-orthogonal linear SOPs after propagation through a 60 km quantum channel, and good agreement with theory. This source, operating in a low power regime, can be used for quantum key distribution (QKD) using polarization-encoding in quantum communications.
We present a single-photon source based on the stimulated four-wave mixing process with adjustable linear state of polarization. This source allowed us to generate non-orthogonal states of polarization, that can be used for quantum key distribution experiments. The average number of photon counts as a function of the angle of the analyzer was obtained for two non-orthogonal linear states of polarization. The results show an accurate detection after propagation through a standard single-mode optical fiber with a length equal to 20 km. We also employed a master/slave configuration between two avalanche photodiodes, in order to check the probability of our single-photon source to emit pulses with more than one photon, for an average number of photons per pulse, μ ∼ 0.2, and consequently the probability of a photon to choose one of the paths. Results show that our experimental scheme is suitable for polarization-encoding experiments.
This thesis begins by proposing the implementation of a probabilistic photon source based on the stimulated four-wave mixing (FWM) process. This source was implemented experimentally and characterized in terms of its statistical distribution. Next, the impact of the stimulated FWM process in a co-propagating quantum signal was studied experimentally. Finally, the violation of Clauser-Horne-Shimony-Holt (CHSH) inequality was experimentally verified using polarization-entangled photon pairs, which were obtained from the spontaneous FWM process in a Sagnac loop. The experimental evolution of the quantum-bit error rate (QBER) in a system without control of polarization, using this degree of freedom to encode information, was studied. It was found out that the QBER increases with the length of the transmission fiber. It was also verified that the increase in the QBER was due to the random rotation of photon’s polarization. A model for the rigorous estimation of the QBER was derived and developed an automatic method to compensate the random rotations of polarization. The method was validated numerically and experimentally, in a transmission system with 40km, showing that it can compensate for the rotations that photons suffer during propagation in optical fibers. Finally, a quantum bit commitment (QBC) protocol between two untrusted entities was implemented. The encoding was performed using two nonorthogonal states of polarization (SOPs). As quantum channel between the two entities, it was first assumed that the transmitter and the receiver were side by side, and after that, they were separated by 8 km and finally, that they were 16km from each other. The implementation of the protocol was performed with a success rate in measurements exceeding 93%, well above the theoretical security limit of 85%. The best strategy for deceiving the commitment was also implemented, and its security experimentally confirmed with a confidence of 7 standard deviations.
Quantum communications can provide almost perfect security through the use of quantum laws to detect any possible leak of information. We discuss critical issues in the implementation of quantum communication systems over installed optical fibers. We use stimulated four-wave mixing to generate single photons inside optical fibers, and by tuning the separation between the pump and the signal we adjust the average number of photons per pulse. We report measurements of the source statistics and show that it goes from a thermal to Poisson distribution with the increase of the pump power. We generate entangled photons pairs through spontaneous four-wave mixing. We report results for different type of fibers to approach the maximum value of the Bell inequality. We model the impact of polarization rotation, attenuation and Raman scattering and present optimum configurations to increase the degree of entanglement. We encode information in the photons polarization and assess the use of wavelength and time division multiplexing based control systems to compensate for the random rotation of the polarization during transmission. We show that time division multiplexing systems provide a more robust solution considering the values of PMD of nowadays installed fibers. We evaluate the impact on the quantum channel of co-propagating classical channels, and present guidelines for adding quantum channels to installed WDM optical communication systems without strongly penalizing the performance of the quantum channel. We discuss the process of retrieving information from the photons polarization. We identify the major impairments that limit the speed and distance of the quantum channel. Finally, we model theoretically the QBER and present results of an experimental performance assessment of the system quality through QBER measurements.
Single photon sources are a key element for quantum computing, quantum key distribution (QKD) and quantum communications. In particular, producing single photons at telecommunications wavelengths is valuable for QKD protocols and would enable realizing the quantum internet. The preferred method for their generation has long been spontaneous down conversion in bulk crystals, which suffers from connection loss to fiber networks. In-fiber spontaneous four-wave mixing provides a viable alternative as a photon pair source due to being compatible with existing fiber networks. We present an all-fiber photon pair source based on degenerate four-wave mixing in a 400 m Highly-Nonlinear fiber, with signal and idler wavelengths generated at 1552.5 nm and 1557 nm respectively. The source consists of CW pump laser operating at 1554.75 nm, which is slightly detuned from the zero group velocity dispersion wavelength into the normal dispersion regime. After pair generation in the highly-nonlinear fiber, three arrayed waveguide gratings are employed to spatially separate signal and idler, and provides a 120 dB pump power reduction. Firstly the source is modelled and experimentally characterized in the well known classical regime of stimulated four-wave mixing. The effect of fiber cooling on spontaneous Raman scattering is modelled and characterized, and a 30% reduction in spontaneous emission is found when cooling the fiber to -77°C. In the low power regime the coincidence to accidental count ratio is simulated and measured. An increase in the coincidence to accidental count ratio is observed when cooling the fiber.